Molded insulating hinge for bipolar instruments

ABSTRACT

An electrosurgical instrument includes a pair of first and second elongated shafts each having an end effector attached to a distal end thereof and a handle. The handle is movable from a first position wherein the end effectors are disposed in spaced relation relative to one another to a second position wherein the end effectors are closer relative to one another. Each of the elongated shafts includes a hinge plate which mounts atop a pivot assembly for effecting movement of the end effectors relative to one another. The instrument also includes a hinge assembly made from an overmold composition which encapsulates and secures the hinge plates and the pivot assembly. The overmold composition is made from an electrically insulating material which insulates the end effectors from one another.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefits of and priority to U.S. ProvisionalPatent Application Ser. No. 60/281,924 entitled: “MOLDED INSULATINGHINGE FOR BIPOLAR INSTRUMENT” which was filed on Apr. 6, 2001 by Sartoret al., the entire contents of this application are hereby incorporatedby reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to joints and hinges which connectmovable components of an electrosurgical instrument and methods forfabricating hinges for movable components of an electrosurgicalinstrument. More particularly, the present disclosure relates to aneasily customizable hinge made from a plastic overmold composition whichconnects two end effectors for relative movement therebetween. Thepresent disclosure also relates to a method for fabricating theovermolded hinge.

2. Background of Related Art

Typically, joints and hinges for electrosurgical instruments whichconnect movable components are formed from an insulating material toprevent shorting between component parts and/or prevent the formation ofalternate current paths through the instrument. As such, instrumentdesigners have manufactured electrosurgical instruments which involvecomplex rotating hinge configurations to isolate, insulate and/orcontrol the electrosurgically active areas of the instrument. Forexample, traditional metal hinge configurations typically includemultiple independent subassemblies which are overmolded with plasticmaterial having high bond strengths. These separately overmoldedsubassemblies are mechanically integrated and arranged in a series ofmanufacturing steps that often require tightly controlled and timeconsuming processes to achieve proper jaw alignment and reliable andconsistent gap separation between electrodes. Moreover, additional stepsare often undertaken to control other parameters associated with therotational movement about the hinge, e.g., friction, torque, etc.

Thus, a continuing need exists for a simple and effective insulatinghinge that can be readily integrated into the manufacturing process toelectrically isolate the movable components of an electrosurgicalinstrument. Further need exists for the development of a simplifiedmanufacturing process which effectively fabricates an electrosurgicalinstrument which includes an insulated hinge that isolates andintegrates the electrically active components of the instrument andresults in the repeated formation of a reliable and easily customizableinstrument which meets specific tolerance requirements for proper jawalignment and gap distances.

SUMMARY

An electrosurgical instrument includes a pair of first and secondelongated shafts each having an end effector attached to a distal endthereof and a handle. The handle is movable from a first positionwherein the end effectors are disposed in spaced relation relative toone another to a second position wherein the end effectors are closerrelative to one another. Each of the elongated shafts includes a hingeplate which mounts atop a pivot assembly for effecting movement of theend effectors relative to one another. The instrument also includes ahinge assembly which is overmolded to encapsulate and secure the hingeplates and the pivot assembly. The hinge assembly is made from anelectrically insulating material which insulates the end effectors fromone another.

Preferably, the hinge assembly is made from a composition of materialsselected from the group consisting of: polyamides, nylon,arcylanitride-butane nitro styrene acetyl, polyesters,syndiotactic-polystryrene (SPS), polybutylene terephthalate (PBT),polycarbonate (PC), acrylonitrile butadiene styrene (ABS),polyphthalamide (PPA), polymide, polyethylene perephthalate (PET),polyamide-imide (PAI), acrylic (PMMA), polystyrene-(PS and HIPS),polyether sulfone (PES), aliphatic polyketone, acetal (POM) copolymer,polyurethane (PU and TPU), nylon with polyphenylene-oxide dispersion andacrylonitrile styrene acrylate. In another embodiment, the hingeassembly is made from a composition of lubricating materials selectedfrom the group consisting of: silicon, molybdenum disulfide and lightolefins.

In one embodiment, the pivot assembly includes a pivot pin integrallyassociated with a first of the hinge plates and a pivot hole formedwithin a second of the hinge plates. Preferably, the pivot pin is madefrom an electrically insulating material. In another embodiment, theovermold composition of the hinge assembly is disposed between the pivotpin and the pivot hole to electrically insulate each of the hinge platesfrom one another.

In yet another embodiment, the hinge assembly includes a retention tabwhich secures the hinge assembly between the hinge plates. Preferably,the retention tab is formed during the overmold process as the overmoldcomposition leaches through the pivot pin to form a tab on theouter-facing surface of the hinge plate. Once the retention tab cures,the hinge assembly is securely held between the hinge plates. In stillyet another embodiment, the hinge assembly includes a stop member forlimiting the movement of the end effectors relative to one another.

The present disclosure also relates to a method of forming a hingeassembly and includes the steps of: providing a pair of first and secondelongated shafts each having an end effector attached to a distal endthereof, a handle and a hinge plate. The handle is dimensioned to effectmovement of the end effectors relative to one another. The methodfurther includes the step of mounting the elongated shafts to a dieblock, introducing an overmold composition into the die block toencapsulate at least a portion of the hinge plates and curing theovermold composition to form the hinge assembly.

In another embodiment, the method further includes the step of:selectively positioning at least one spacer between the end effectors tomaintain a gap distance between the end effectors during the molding andcuring step.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the presently disclosed surgical instrumenthaving a molded insulating hinge assembly are described herein withreference to the drawings, wherein:

FIG. 1 is a perspective view of one embodiment of a bipolar forcepshaving a molded insulating hinge assembly constructed in accordance withthe present disclosure;

FIG. 2A is an enlarged, right, side view of an end effector of thebipolar forceps of FIG. 1 prior to overmolding;

FIG. 2B is a bottom view of the end effector of FIG. 2A;

FIG. 2C is a left, side view of the end effector of FIG. 2A;

FIG. 3A is an enlarged, right, side view of a second end effector of thebipolar forceps of FIG. 1 prior to overmolding;

FIG. 3B is a bottom view of the end effector of FIG. 3A;

FIG. 3C is a left, side view of the end effector of FIG. 3A;

FIG. 4 is an exploded, perspective view of the bipolar instrument ofFIG. 1; and

FIG. 5 is a perspective view of the embodiment shown in FIG. 1 shownwith a spacer disposed between a pair of jaw members to fix a specificgap distance during the overmolding process.

DETAILED DESCRIPTION

Referring now in specific detail to the drawings in which like referencenumerals identify similar or identical elements throughout the severalviews, and initially to FIGS. 1-3C, one particular embodiment of anelectrosurgical instrument 10 includes two elongated shafts 30 and 60each having a distal end effector 32, 62 and a proximal handle portion34 and 64, respectively. Handles 34 and 64 are movable relative to oneanother about a hinge assembly 20 from a first position wherein thedistal end effectors 32, 62 are positioned in spaced relation relativeto one another to a second position in which the distal end effectors32, 62 cooperate to grasp tissue therebetween. It is envisioned thathandles 34 and 64 may take any design configuration suitable formanipulation or control of the surgical instrument 10.

Each distal end, e.g., 32, has a jaw member 36 disposed at the distalend thereof which includes a tissue grasping surface 38 dimensioned tocooperate with the other jaw member, e.g., 66, and other tissue graspingsurface, e.g., 68, to grasp tissue and other luminal structures uponactuation of the handles 34 and 64. The jaw members 36, 66 each alsoinclude a hinge plate 35, 65, respectively, which cooperate to supportopposing sides of the hinge assembly 20 as explained in more detailbelow. Hinge plate 35 includes a pivot pin 74 which mechanically engagesa corresponding pivot hole 61 disposed within hinge plate 65 to formpivot assembly 70.

Hinge assembly 20 as described herein relates to one particularembodiment for use with a bipolar electrosurgical forceps 10, however,it is contemplated that the presently disclosed hinge assembly 20 couldbe dimensioned for use with other electrosurgical instruments includingvessel sealing instruments, grasping instruments, ablation instruments,electrosurgical scissors, etc. Moreover, it is also envisioned that thehinge assembly 20 may be configured for use with a broad range of othernon-electrical surgical instruments such as pliers, scissors, shears,crimpers and wire cutters.

Preferably, hinge assembly 20 is made from a composition 25 ofinsulating material such as plastic which is overmolded to encapsulatethe hinge plates 35, 65 during the manufacturing process. As best seenin FIG. 2C, pivot pin 74 includes a reinforcing portion 72 which allowsthe mold composition 25 to extrude through the pivot pin 74 of hingeplate 35 to an opposite side 63 of hinge plate 65 to form a retentiontab 50. More particularly, after a significant amount of moldcomposition 25 is extruded around the reinforcing portion 72 of thepivot pin 74, the retention tab 50 is stamped against the opposite side63 of hinge plate 65 to secure the hinge plates 35 and 65 in closeabutment about the pivot assembly 70. As can be appreciated in thisembodiment of the present disclosure, the mold composition 25 iscontiguous with the exterior of the hinge plate 35 through aperture 31,around reinforcing portion 72 and with the retention tab 50 whichsecurely engages the hinge assembly 20 between the hinge plates 35, 65.

As can be appreciated, both the mold composition 25 and the retentiontab 50 are formed during the same molding step resulting in theformation of the hinge assembly 20. It is envisioned that once cured,the retention mechanism 50 forms a structural limit that at leastpartially controls the alignment of the distal end effectors 32 and 62as well as the amount of pivotal movement between the jaw members 36 and66. Alternatively, the retention tab 50 may be made from the same or adifferent mold composition 25 and is designed to mechanically engage thepivot pin 74 or the hinge plate 65 to secure the hinge assembly betweenthe hinge plates 35 and 65.

As best shown in the exploded view of FIG. 4, the formation of the hingeassembly 20 in this manner electrically isolates the two end effectors32 and 62 and the component parts thereof enabling a user to selectivelyapply electrosurgical energy through the tissue and between the jawmembers 36 and 66 as needed. More particularly, during the overmoldprocess, the plastic cures about the outer periphery 75 of pivot pin 74which electrically isolates hinge plate 35 from hinge plate 65. As canbe appreciated, the retention tab 50 which, as mentioned above, is alsoformed of plastic which extrudes through pivot pin 74 to the oppositeside 63 of hinge plate 65, not only retains the two hinge plates 35 and65 in secure abutment about the pivot assembly 70 but also electricallyisolates the hinge plates 35 and 65 from one another.

Because the presently disclosed hinge assembly 20 is preferably formedduring a single manufacturing step, it can be easily customized anddimensioned to suit a particular purpose or to achieve a particularresult. For example, the alignment of the jaw members 36 and 66, e.g.,jaw angle or jaw offset, may be easily customized depending upon aparticular purpose. Moreover, the formation of a gap distance betweenthe jaw members 36, 66 may be easily customized. For example, the hingeassembly 20 may be molded or formed during the manufacturing processsuch that the jaw members 36 and 66 maintain a consistent and specificgap distance within the range of about 0.001 inches to about 0.005inches at closure. The formation of the gap distance is discussed belowwith particular reference to FIG. 5.

Generally, hinge 20 is formed from an overmold composition containing ajoint-forming base resin material and a lubricating component.Hinge-forming materials for use herein can be any commercially availablematerials known to one skilled in the art for toughness and strength aswell as being capable of injection molding. Suitable joint-forming baseresin materials include, but are not limited to, polyamides such asnylon, arcylanitride-butane nitro styrene; acetyl, polyesters, etc.Preferably, the overmold composition is made from a plastic orplastic-based material having a Comparative Tracking Index of about 300volts to about 600 volts for dielectric isolation. For example, theovermold composition 25 may be made from a group of materials selectedfrom a group which includes Nylons, Syndiotactic-polystryrene (SPS),Polybutylene Terephthalate (PBT), Polycarbonate (PC), AcrylonitrileButadiene Styrene (ABS), Polyphthalamide (PPA), Polymide, PolyethyleneTerephthalate (PET), Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene(PS and HIPS), Polyether Sulfone (PES), Aliphatic Polyketone, Acetal(POM) Copolymer, Polyurethane (PU and TPU), Nylon withPolyphenylene-oxide dispersion and Acrylonitrile Styrene Acrylate.Alternatively, it is envisioned that a non-plastic insulating material,e.g., ceramic, may be used in lieu of or in combination with one or moreof the above-identified materials to facilitate the manufacturingprocess and possibly contribute to more uniform and consistent transferof electrosurgical energy across the tissue.

Suitable lubricating components for use with the base resin materialinclude a broad range of materials known to compliment the overmoldcomposition to provide mold having a low bonding strength with goodsurface lubricating qualities. Such lubricating components include, butare not limited to, silicon-like materials, molybdenum disulfide, lightolefins, etc. Depending upon the overall composition of the base resinmaterial being used, a lubricating component may not be required.

It is also anticipated that additional materials may be employed incombination with the above materials to achieve suitable levels oftoughness and strength in the molded hinge 20. These additionalmaterials may include, for example, reinforcing agents such as glassfibers, ground glass, or elongated glass fibers. For example, in oneparticular embodiment, hinge assembly 20 is formed from a commerciallyavailable nylon material having about 2.5 wt. % glass fiber reinforcingmaterial and a silicone lubricating component in the range of about 0.75wt. % to about 10 wt. %. In another embodiment, hinge assembly 20 may beformed from a nylon having glass fiber reinforcing material in the rangeof about 5 wt. % to about 40 wt. % and silicone in the range of about 2wt. % to about 8 wt. %.

While silicone or other lubricating agents are typically used ininjection molding processes, it has been found that the amount ofsilicone should be tightly controlled to provide uniform and consistentcuring and operating efficiencies. It is envisioned that the siliconecomponent of the overmold composition creates a sustained lubricatedsurface at the interface between hinge plates 35 and 65. It has alsobeen found that increasing the level of silicone, e.g., amounts greaterthan 2 wt.%., in the joint-forming material of hinge assembly 20,produces an overmold composition having a low bond strength. As can beappreciate, although the overmold composition 25 has a low bond strengthto the surrounding metals, i.e., elongated shafts 30, 60 and hingeplates 35, 65, the low bonding strength is offset by a the mechanicaladvantages of the retention tab 50 and aperture 31.

As mentioned above, the presently disclosed hinge assembly 20 may beformed during a single manufacturing step and may be easily customizeddepending upon a particular purpose or to achieve a particular result.For example, parameters such as self lubrication of the hinge assembly20, hinge assembly 20 strength, jaw member 36, 66 alignment, e.g., jawangle or jaw offset, isolation of the jaw members 36 and 66 duringelectrosurgical application and the formation of a gap distance betweenthe jaw members 36 ad 66 (or electrodes or probes attached to the jawmembers 36 and 66) may be easily achieved.

The present application is not limited to the above identifiedmaterials, but contemplates a broad range of overmold composition 25 invarying combinations and amounts that provide an overmold compositionsuitable for the function of hinge assembly 20. It is envisioned thatapplications described herein relating to the injection overmolding ofthermoplastic polyamides, for example, may be translated into otherareas including, but not limited to, other engineering plasticmaterials, engineering metals and ceramics that may be selectivelyapplied in varying insulative as well as mechanical applications.

The overmold composition 25 of the present disclosure is configured tocreate a tough and strong hinge assembly 20 by at least partiallyencapsulating the hinge plates 35 and 65 and the pivot assembly 70 (andthe various components thereof. The overmold composition 25 providessuitable strength as a result of its continuity of encapsulation as wellas the ability of the overmold composition 25 to form surface featureswhich are specifically dimensioned to improve the strength of the hingeassembly 20 once cured. For example, features within the pivot pin 74and features within the pivot hole 61 may be provided to increase theoverall strength of the instrument and/or hinge assembly 20, e.g.notches, detents, cavities, overmolded posts, etc. Further, structuralstrength for the hinge assembly 20 may be gained by coating or fillingfeatures defined in the surface of the hinge plates 35, 65 to augmentthe mechanical bonding of the plastic mold with the hinge plates 35, 65,pivot pins 74 and pivot holes 61. For example, surface undulations suchas lip structures, overhanging shapes, concave shapes, or cantileveredstructures having different geometric shapes may be employed tomechanically engages the hinge assembly 20 to the hinge plates 35.

Preferably, the elongated shafts 30, 60 are made from a stainless steelmaterial. However, other metal alloys, plastics, ceramics, or compositesare also contemplated including combinations of one or more plastics,composites, metals, graphite, carbon-coated plastics and/or any otherconductive materials which are well suited for overmolding purposes.Preferably, the elongated shafts 30 and 60 are die-cut, stamped, ormicro-machined such that the end effectors 32 and 62 and the hingeplates 35 and 65 from integral parts thereof. As can be appreciated,making these elements integral and utilizing the overmold hinge assembly20 as presently disclosed herein greatly simplifies the overallmanufacturing and assembly processes.

Instrument 10 may also include surface treatments (e.g., nylon powdercoatings, chemical treatments, nickel alloy coatings, mechanical finishtreatments, shrink tubing, etc.) which facilitate manipulation of thetissue structures, enhance conduction of electrosurgical energy acrossthe jaw members 36, 66 and/or reduce the likelihood of inconsistenciesacross the treatment area which may lead to collateral tissue damage,flashover, thermal spread, arcing, etc.

Preferably, the thickness of the hinge assembly 20 can be selectivelyaltered depending upon a particular purpose or for use with a certaininstrument. The ultimate thickness and strength of the overmoldcomposition 25 is also related to the viscosity of the overmoldcomposition 25 and the duration and temperature of the curing process.For example, the hinge assembly 20 may include a range of thickness fromabout 0.020 to about 0.040 inches in thickness. The thickness of theovermold composition 25 also depends on mechanical load bearing anddimensional requirements of a particular application.

As best shown in FIG. 4, the outer periphery 75 of pivot pin 74 providesa basis for the formation of additional molded material around the pivotpin 74 which not only electrically insulates the jaw members 36 and 66from one another but also reduces the chances of the pivot slipping orrotating when torquing, cross-loading, or shearing forces are appliedduring the normal use of instrument 10.

It is envisioned that the hinge assembly may be designed as a morecomplex mechanism and/or may be designed to encapsulate a more complexpivoting mechanism. For example, it is contemplated that the hingeassembly 20 may include various multiple-link systems such as a two-bar,three-bar or four-bar linkage or may include a two-step hinge. The pivotpin 74 and/or the pivot hole 61 may also be dimensioned in a variety ofdifferent shapes and sizes depending upon a particular purpose or toachieve a particular result, e.g., cam and cam-follower, arcuate,elliptical, etc. It is also envisioned that the hinge assembly 20 mayinclude one or more stop members 19 which limit the overall distancethat the jaw members 36, 66 may pivot in either the open or closedpositions. The stops 19 may be configured in steps or as a cantileveredfeature to define more than one gap distance between jaw members 36 and66.

In one embodiment, retention tab 50 may be configured to mechanicallyengage a portion of the hinge plate 65 and/or pivot pin 74 which iscontemplated to serve two purposes: 1) to mechanically retain theretention tab 50 against the hinge plate 65 and further secure theinstrument 10 as assembled; and 2) to bias the pivot assembly 70 to apredetermined open, closed, or intermediary position. For example, theouter-facing surface 63 of hinge plate 65 may be provided with slots orgrooves (not shown) which mechanically engage the retention tab 50.

With respect the to particular surgical instrument of FIGS. 1-4, i.e.,bipolar forceps 10, first and second conductive wires 41 and 45 are eachelectrically coupled to a respective distal end effector 32 and 62 atone end thereof and ultimately connected to an electrosurgical generator(not shown) at the opposite end thereof. The first electrical conductor41 (see FIG. 2A) connects the first jaw member 36 to a first electricalpotential and the second electrical conductor 45 (see FIG. 3A) connectsthe second jaw member 66 to a second electrical potential. Preferably,the first and second electrical conductors 41 and 45 are disposed withinlongitudinally-oriented channels defined within elongated shafts 30 and60, respectively. The channels are preferably oriented and dimensionedto facilitate mechanical engagement of the electrical conductors 41 and45 with the respective jaw members 36 and 66 in such a manner to allowfree, pivotable movement of the jaw members 36 and 66 relative to oneanother. Preferably, the cable leads are attached to the electricallyconductive jaw members 36 and 66 by a crimp-like electrical connection(not shown). As mentioned above, the hinge assembly 20 includes at leastone stop 19 which abuts against elongated shafts 30, 60 to preventover-rotation of the jaw members 36 and 66 to avoid straining theelectrical leads.

Preferably, hinge assembly 20 is manufactured in a single injectionmolding or manufacturing process step in which elongated shafts 30 and60 are mounted atop a die block within an injection molding machine. Theovermold composition 25 of the hinge assembly 20 is then injectedbetween the jaw members 36 and 66 to encapsulate the hinge plates 35 and65 and the pivot assembly 70. As mentioned above, the hinge assembly 20is strengthened by the continuity of the plastic overmold composition 25which extrudes through the pivot pin 74 and pivot hole 61 to form theretention tab 50. Thus, in one particular embodiment, the hinge assembly20 is completely formed by overmold composition flowing around andthrough the various components parts of the hinge assembly 20 and thepivot assembly 70. As mentioned above, the retention tab may be aseparate component made from the same or a similar composition which isdimensioned to mechanically engage the pivot pin 74 or the outer-facingsurface 63 of the hinge plate 65.

As mentioned briefly above and as shown in FIG. 5, a spacer 100 may bepositioned between jaw members 36 and 66 prior to the overmoldingprocess. The spacer 100 sets a fixed gap distance “G” between jawmembers 36 and 66 at closure (i.e., when the jaw members 36 and 66 aredisposed in the closed or tissue grasping position) by limiting theformation of the stop 19 during the overmolding process. As can beappreciated, different and/or customized gap distances “G” between thejaw members 36 and 66 can be easily formed depending upon a particularpurpose or to achieve a particular result.

The presently disclosed overmolding process also enables themanufacturer to customize the precise alignment of the jaw members 36and 66 relative to one another. Thus, in applications in which thealignment of jaw members 36 and 66 is critical, such as for shearing,cutting and sealing, the accuracy, alignment and configuration of thehinge assembly 20, pivot assembly 70 and jaw members 36 and 66 can beeasily customized. Further, the presently disclosed process alsoprovides a repeatable and reliable alignment tool for mass manufacturingof surgical instruments according to specific tolerances.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the present disclosure. For example, it is contemplated that hingeassembly 20 can be configured to join a plurality of differentcomponents or subassemblies in the assembly depending upon a particularpurpose. Moreover, the outer periphery 75 of pivot pin 74 could alsoinclude features such as a series of undulations or knurling, or aseries of radially aligned cavities having features within thosecavities that strengthen the mechanical interface of the overmoldcomposition to the pivoting assembly 70.

In one embodiment, the instrument includes a conductive strip (notshown) disposed through one shaft, e.g., shaft 30. Electrosurgical wiresor cables (not shown) from an electrosurgical generator (not shown)connect the two electrical potentials to the conductive strip. Theopposite end of the conductive strip includes one electrical connectionto end effector 32 and a second electrical connection to pivot assembly70 which provides electrical continuity to the opposite end effector 62.More particularly, the second electrical connection of the conductivestrip makes contact across the moving junction of the pivot assembly. Itis not necessary that the conductive strip wrap around the pivot pin 74between the instrument halves because during the molding process theconductive strip is forced into intimate contact with the opposite endeffector 62, i.e, the flow of the uncured hinge material positions theconductive strip into contact with end effector 62.

As a result thereof, secondary washers or force loading devices are notrequired to initiate contact between the conductive strip and theopposite end effector 62. The conductive strip my also include a seriesof wave-like folds, e.g., accordion folds, which give the conductivestrip a spring-like quality and which fosters contact with the oppositeend effector 62 during and after curing. As can be appreciated, thisarrangement assures that a moving or sliding contact is maintainedbetween the conductive strip and the end effector 62 during movement,i.e., pivoting, of the end effectors relative to one another.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplications of preferred embodiments. Those skilled in the art willenvision other modifications within the scope and spirit of the claimsappended hereto.

1. An electrosurgical instrument comprising: first and second elongatedshafts each having an end effector attached to a distal end thereof anda handle, said handles being movable from a first position wherein theend effectors are disposed in spaced relation relative to one another toa second position wherein the end effectors are closer relative to oneanother; each of said elongated shafts including a hinge plate whichmounts atop a pivot assembly for effecting movement of the end effectorsrelative to one another; and a hinge assembly formed from an overmoldcomposition which, when cured, encapsulates said hinge plates, saidovermold composition being made from an electrically insulating materialwhich insulates each of said end effectors from one another.
 2. Anelectrosurgical instrument according to claim 1 wherein said pivotassembly includes a pivot pin integrally associated with a first of saidhinge plates and a pivot hole formed within a second of said hingeplates, said pivot pin being made from an electrically insulatingmaterial.
 3. An electrosurgical instrument according to claim 1 whereinsaid pivot assembly includes a pivot pin integrally associated with afirst of said hinge plates and a pivot hole formed within a second ofsaid hinge plates, said overmold composition of said hinge assembly whencured being disposed between said pivot pin and said pivot hole toelectrically insulate each of said hinge plates from one another.
 4. Anelectrosurgical instrument according to claim 1 wherein said overmoldcomposition of said hinge assembly includes materials selected from thegroup consisting of polyamides, nylon, arcylanitride-butane nitrostyrene acetyl, polyesters, syndiotactic-polystryrene (SPS),polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrilebutadiene styrene (ABS), polyphthalamide (PPA), polymide, polyethyleneperephthalate (PET), polyamide-imide (PAI), acrylic (PMMA), polystyrene(PS and HIPS), polyether sulfone (PES), aliphatic polyketone, acetal(POM) copolymer, polyurethane (PU and TPU), nylon withpolyphenylene-oxide dispersion and acrylonitrile styrene acrylate.
 5. Anelectrosurgical instrument according to claim 4 wherein said overmoldcomposition of said hinge assembly includes lubricating materialsselected from the group consisting of silicon, molybdenum disulfide andlight olefins.
 6. An electrosurgical instrument according to claim 1wherein said hinge assembly includes a retention tab which secures saidhinge assembly between said hinge plates.
 7. An electrosurgicalinstrument according to claim 4 wherein said pivot assembly includes apivot pin integrally associated with a first of said hinge plates and apivot hole formed within a second of said hinge plates, said pivot pinincluding a reinforcing portion disposed therein which permits saidovermold composition of said hinge assembly to extrude through saidpivot pin to form a retention tab for securing said hinge assemblybetween said hinge plates.
 8. An electrosurgical instrument according toclaim 1 wherein said hinge assembly includes a stop member for limitingthe movement of said end effectors relative to one another. 9.(canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. Anelectrosurgical instrument comprising: first and second elongated shaftseach having an end effector attached to a distal end thereof and ahandle, said handles being movable from a first position wherein the endeffectors are disposed in spaced relation relative to one another to asecond position wherein the end effectors are closer relative to oneanother; each of said elongated shafts including a hinge plate thatmounts atop a pivot assembly for effecting movement of the end effectorsrelative to one another; a hinge assembly formed from an overmoldcomposition that, when cured, encapsulates said hinge plates, saidovermold composition being made from an electrically insulating materialthat insulates each of said end effectors from one another; and thehinge assembly including a stop member for limiting the movement of saidend effectors relative to one another.